CCP-CPP GMR read heads are considered as promising candidates for 180 Gb/in2 and higher magnetic recording densities. This increase in recording density requires the reduction of the read head dimensions. For example, for 180 Gb/in2, dimensions around 0.1×0.1 microns are required. A CPP read head can be considered functional only if a significant output voltage, Vout, can be achieved when the head senses the magnetic field of a recorded medium. If DR/R is defined as the percentage resistance change, at constant voltage, under the magnetic field for the sensor and V is the voltage applied across the sensor (BHV), then Vout=DR/R×V.
Referring now to FIG. 1, we show there the main features of a CCP-CPP GMR (current confined path-current perpendicular to plane giant magneto resistance) read head device (as well as bottom and top leads 11a and 11b respectively). These are an anti-ferromagnetic (pinning) layer 12, which may include a seed layer (not shown), pinned layer 14 (usually a tri-layer that acts as a synthetic AFM, but shown here as a single layer), a non-magnetic spacer layer 15 (which will be discussed further below), a free layer 16, and a capping layer 17.
When the free layer is exposed to an external magnetic field, the direction of its magnetization is free to rotate according to the direction of the external field. After the external field is removed, the magnetization of the free layer will stay at a direction, which is dictated by the minimum energy state, determined by the crystalline and shape anisotropy, current field, coupling field and demagnetization field. If the direction of the pinned field is parallel to the free layer, electrons passing between the free and pinned layers, suffer less scattering. Thus, the resistance at this state is lower. If, however, the magnetization of the pinned layer is anti-parallel to that of the free layer, electrons moving from one layer into the other will suffer more scattering so the resistance of the structure will increase. The change in resistance of a spin valve is typically 5-15%.
In the foregoing discussion it was tacitly implied that non-magnetic spacer layer 15 is a homogenous layer of a single conductive material. In the CCP (current confined path) design, the spacer layer is actually a trilayer of two conductive layers (such as copper) with a very thin insulating layer between them. The latter is typically between about 5 and 15 Angstroms thick and includes a limited number of metal paths within itself. Thus, current through the spacer layer is confined to those areas where the two conductive layers contact one another via these metal paths (shown schematically in FIG. 1 as the hatched areas within layer 15).
As can be seen in FIG. 2a, layer 15 is formed by first laying down copper layer 21 followed by AlCu layer 22. Through the addition of several novel features the technology for manufacturing CCP-CPP GMR has been greatly improved. However, there remains some concern with regard to electromigration (EM) in these CCP-CPP GMR devices. The present invention discloses a variety of ways to overcome this problem.
A routine search of the prior art was performed with the following references of interest being found:
U.S. Pat. No. 6,560,077 (Fujiwara et al) teaches that a current-confining path is formed in an insulating layer of a GMR-CPP. U.S. 2005/0002126 (Fujiwara et al) discloses a current-confining layer structure formed of a conductor and an insulator. The conductor may be Al, Mg, Cr, Cu, etc. U.S. 2005/0152076 (Nagasaka et al) teaches that oxidation of an magnetic layer results in a current-confining effect. Oxidation of a magnetic intermediat elayer such as CoFe between two layers of Cu is taught. U.S. 2005/0094317 (Funayama) and 2005/0052787 (Funayama et al) show a current control region comprising AlOx and Cu. Mg or Cr could be used with a copper content of 1% to 50%.
U.S. 2004/0190204 (Yoshikawa et al) shows an intermediate layer comprising Cu/oxidized AlCu/Cu where AlCu is oxidized by IAO. U.S. 2003-0053269 (Nishiyama) teaches that a non-magnetic layer functions as a current confining layer. This layer may be Al203, Si02, or Ta02. U.S.2005.0122683 (Nowak et al) describes forming current-confining paths in the MR stack.